Cards may be "topped-up" by recurring payment authority, by online purchase, at credit card terminals or by cash, the last two methods at stations or ticket offices.The card is designed to reduce the number of transactions at ticket offices and the number of paper tickets.Usage is encouraged by offering substantially cheaper fares than with cash though the acceptance of cash is being phased out. The card was first issued to the public in July 2003 with a limited range of features and there continues to be a phased introduction of further functions.

The Oyster card is a form of electronic ticketing used on public transport in Greater London in the United Kingdom.

It is promoted by Transport for London and is valid on travel modes across London including London Underground, London Buses, the Docklands Light Railway (DLR), London Overground, trams, some river boat services, and most National Rail services within the London fare zones.

A standard Oyster card is a blue credit-card-sized stored-value contactless smartcard that can hold single tickets, period tickets and travel permits, which must be added to the card before travel.

Passengers touch it on an electronic reader when entering and leaving the transport system in order to validate it or deduct funds.

The intellectual property rights to the Oyster brand originally belonged to Transys.

Following the renegotiation of the operating contract in 2008, Tf L sought to retain the right to use the Oyster brand after the termination of its partnership with Transys, The Oyster card has a claimed proximity range of about 80 mm (3 inches).

The card operates as a RFID system and is compatible with ISO/IEC 14443 types A and B.

The Oyster card was set up under a Private Finance Initiative (PFI) contract between Tf L and Tran Sys, a consortium of suppliers that included EDS and Cubic Transportation Systems (responsible for day-to-day management) and Fujitsu and WS Atkins (shareholders with no active involvement).

The Oyster name was agreed on after a lengthy period of research managed by Tran Sys and agreed by Tf L.